1. Field of the Invention:
The present invention relates to an electronic component that includes a capacitor provided on a substrate, for example formed by semiconductor processing technology.
2. Description of the Related Art:
In a radio frequency (RF) system such as a mobile phone or a wireless LAN, signals are subjected to phase-matching for satisfactory transmission among functional devices constituting the system. Accordingly, the input/output (I/O) terminal of each device is provided with a passive element that includes a passive component such as an inductor or a capacitor, and that acts as a phase shifter for controlling the phase of the signals.
In the RF system, a SAW filter is employed for use as a narrow-band frequency filter. The SAW filter, which includes a piezoelectric element, produces a difference in potential between piezoelectric element electrodes because of a piezoelectric effect, when a physical impact or a thermal effect is applied to the SAW filter or the piezoelectric element thereof during the manufacturing process of the apparatus in which the SAW filter is incorporated. In this case, a predetermined voltage is applied to an electronic component electrically connected to the SAW filter. The capacitor included in the passive element (phase shifter) is usually electrically connected to the SAW filter, and hence the capacitor has to have a high withstanding voltage (e.g. 150 V or higher), to prevent a dielectric breakdown between the capacitor electrodes, which may occur upon application of a voltage accidentally generated by the SAW filter or the piezoelectric element thereof.
There has been a constant demand for reduction in dimensions of various parts composing RF systems, driven by the increase in number of parts for achieving a higher performance. For making the system smaller in dimensions, an integrated passive device (hereinafter, IPD) manufactured based on a semiconductor processing technology, which includes a plurality of predetermined passive components such as an inductor, a capacitor, a resistor and a filter densely integrated therein, may be employed the passive element (phase shifter). When employing the IPD, the capacitor included therein still has to have a high withstanding voltage, for preventing a dielectric breakdown between the capacitor electrodes, as stated above. Techniques related to the IPD are found, for example, in JP-A-H04-61264 and JP-A-2002-33239.
FIG. 9 is a schematic cross-sectional view showing a part of a conventional IPD 90. The IPD 90 includes a substrate 91, a plurality of passive components each including a capacitor 92, integrated on the substrate 91, an wiring 93 and a protecting film 94. The capacitor 92 has a multilayer structure including an electrode film 92a (lower electrode film), an electrode film 92b (upper electrode film), and a dielectric film 92c. The wiring 93 includes a joint portion 93a connected to the electrode film 92b. 
The electrode film 92b has a thickness of approximately 1 μm. For forming the electrode film 92b, a conductor film, which is to subsequently serve as the electrode film 92b, is formed on the substrate 91 to cover the electrode film 92a and the dielectric film 92c already formed on the substrate 91. A resist film given a pattern corresponding to the electrode film 92b is then provided on the conductor film, and an ion milling process is performed utilizing the resist film as the mask, thus to shape the conductor film according to the pattern. When performing such subtractive process to form the electrode film 92b, the thinner the conductor film, or the electrode film 92b is, the more accurately the electrode film 92b can be formed in pattern (hence in area). The precision in area of the electrode film 92b affects the precision in static capacitance of the capacitor 92, which is why the electrode film 92b is formed in a thickness of approximately 1 μm in the conventional IPD 90, for achieving high precision in static capacitance.
In contrast, the wiring 93 (including the joint portion 93a) is formed in a relatively greater thickness. Making the wiring 93 thicker can reduce a resistance thereof, and the reduction in resistance is preferable from the viewpoint of reducing a signal loss through the IPD 90. Accordingly, the wiring 93 is formed in a thickness of approximately 10 μm for example.
The capacitor 92 of the conventional IPD 90, however, often has a withstanding voltage below a practically acceptable level, which has to be addressed. For improving the withstanding voltage of the capacitor 92, it could be an option to form the dielectric film 92c in a greater thickness. Increasing the thickness of the dielectric film 92c, however, requires increasing the area of the electrode film 92b, because otherwise the static capacitance of the capacitor 92 cannot be maintained. Therefore, it is not preferable to increase the thickness of the dielectric film 92c, from the viewpoint of suppressing an increase in dimensions of the capacitor 92, hence the IPD 90.